In recent years, water resistant supports in which both sides of a sheet of raw paper are coated with polyolefins such as polyethylene have been preferred as photographic printing paper supports, with the aim of preventing treatment solutions from permeating in photographs at the time of their development and fixing, as well as the aim of shortening processing times for washing, drying and the like.
With regard to raw paper, on the other hand, an anionic sizing agent, an anionic paper strength improving agent and, with the aim of fixing these anionic chemicals to pulp materials, an inexpensive aluminum salt have been used as additives in paper materials during paper making processes. Since the use of such additives results in an acidic condition, this kind of raw paper is generally called acidic paper.
In recent years, however, neutral paper has been used more commonly because of its many advantages in terms of the shelf life, improvement of raw paper strength, closing of white water during papermaking processes, prevention of corrosion of facilities and the like.
In raw paper for use as a support in photographic printing paper, it is necessary to use highly sized paper for the purpose of preventing the permeation of developing solution into the support through its cut edges at the time of the processing. As a consequence, when neutral paper is used as a raw paper support for use in photographic printing paper, it is important to employ an alkyl ketene dimer having a self-fixing ability as a sizing agent, as well as a cationic polyacrylamide as a paper strengthening agent (see Japan Tappi Journal, vol.41, no.10, p 81 (1989)). In such an instance, papermaking at a neutral range (pH of paper material is between 6.0 and 7.5) has some disadvantages, such as increased drying load due to inferior wetting on a wire compared to the case of papermaking at an acidic range (pH of paper material is at least 3.5 and less than 6.0), as well as the generation of stains on press rolls and the like and the slippery surface of prepared raw paper due to the use of an alkyl ketene dimer as a sizing agent.
With the aim of overcoming the aforementioned problems involved in the art, the inventors of the present invention have conducted intensive studies and found that excellent wetting on a wire and prevention of stain generation during papermaking processes at a neutral pH range can be achieved by the use of a specific cationic polyacrylamide resulting from the copolymerization of acrylamide and a cationic monomer and, as required, an epoxidized higher fatty acid amide, and that a photographic printing paper support obtained by coating both sides of the thus prepared raw paper with a polyolefin resin can prevent the permeation of developing solution through the cutting edge of the support to a marked level. The present invention has been accomplished as a result of these efforts.